1. Field of the Invention
The invention relates to control systems in which the purpose is to generate an analog reversible polarity signal related in amplitude to a variable shaft angle position and more particularly to control systems using shaft angle controlled synchro resolver devices for producing such reversible polarity signals related to the variable shaft angle position and independent of variations in the amplitude of the electrical carrier excitation of the synchro resolver and of spurious phase shifts seated therein.
2. Description of the Prior Art
One of the known prior art synchro resolver systems for generating a variable polarity analog voltage proportional to the position of a shaft solves the equation: EQU V.sub.o =KE (1-cos .theta.+.vertline.sin .theta..vertline.).
Where V.sub.o is the desired analog voltage, K is ideally a proportionality constant, E is the synchro excitation carrier peak amplitude and .theta. is the relative shaft angle. However, variation of the carrier peak amplitude E in this prior system causes the proportionality factor K to change undesirably and there are also produced discontinuities in the output analog signal when the shaft angle .theta.=.+-.45.degree.. The dependence of V.sub.o on the unconstant voltage E in the foregoing equation can be removed by continuously sensing the value of E and by performing a corrective electronic division only at the cost of additional equipment.
A second method converts the synchro resolver cosine .theta., sine .theta. output data into one phase shifted signal and utilizes a phase detector to provide the desired variable polarity output signal. Gradient errors due to the undesired dependence of V.sub.o on E are eliminated and discontinuity effects are reduced. However, intermediately generated variable phase shift errors arising especially in the synchro resolver disadvantageously reduce the accuracy of this second technique. Accordingly, the present invention is considered to be a significant one over prior art concepts such as that of the R. E. Thomas U.S. Pat. No. 4,093,903, issued June 6, 1978 and assigned to Sperry Rand Corporation and over systems of the kind such as that disclosed in the K. G. Martin U.S. Pat. No. 3,701,936. While such prior systems have found utility in some degree, it is desired to avoid any system in which the output can be a function of the peak excitation of the synchro resolver, and to avoid the abrupt discontinuities present when the designer elects to use switching between input trigonometric functions. While the Thomas and Martin references strive to deal with the problem of extending the angular operation of a resolver, they also deal without major success with the problem solved by the present invention.